1. Field of the Invention
The present invention relates to a polydimethylsiloxane-modified urethane resin derivative and a dimethylsiloxane-modified urethane coating resin composition which are useful for applications such as a coating composition, a binder, an adhesive and a sealant, and a method for curing the composition.
2. Description of the Related Art
A polyurethane resin can be prepared by reacting a polymer or a monomer having a hydroxyl group in a molecule with a polymer or a monomer having an isocyanate group in a molecule. This resin is usually excellent in flexibility, adhesive properties, coating film formability and the dispersibility of a pigment or the like, and therefore it is often used as a binder for a coating composition, an ink base, an adhesive and a sealant.
Furthermore, for the purpose of more suitably fitting the polyurethane resin to these uses, or for the purpose of further enlarging the utilizable range of the polyurethane resin in addition to the above uses, it has been heretofore investigated that a silicone is added to the polyurethane resin to modify this resin, thereby imparting characteristics such as mold release properties, sliding properties and water repellency to the polyurethane resin.
As techniques for modifying the polyurethane resin with the silicone, there are known (a) a method which comprises reacting a mixture of a dimethyl silicone oil and a polymer having a hydroxyl group with a resin containing an isocyanate to prepare a silicone oil-modified polyurethane resin (Japanese Patent Publication No. 470/1988 and Japanese Patent Application Laid-open No. 176639/1986), (b) a method which comprises copolymerizing a monomer having a hydroxyl group, a monomer having an isocyanate group and a dimethylsilcone having a polymerizable functional group to prepare a silicone-modified polyurethane resin (Japanese Patent Application Laid-open Nos. 249821/1989 and 238315/1985), (c) a method which comprises grafting a reactive silicone having a functional group such as an isocyanate group which can easily react with a hydroxyl group, on the hydroxyl group present in the polyurethane resin to prepare a silicone-modified polyurethane resin (Japanese Patent Application Laid-open No. 116390/1994).
However, according to the method (a) just described, compatibility between the dimethylsiloxane and the other components is low, and for this reason, when this modified polyurethane resin is used for coating, there are some problems, and for example, the resulting coating film is opaque and the surface state of the film is not smooth. In addition, even if the compatibility can be improved, the silicone oil bleeds out from the coating film with the lapse of time, because the silicone oil does not chemically bond to the polyurethane resin. In consequence, the desired object cannot be achieved inconveniently.
Furthermore, in the case of the above method (b) in which the silicone oil is introduced into the main chain of the resin by the copolymerization, the mechanical strength of the obtained polyurethane resin is impaired on occasion.
Additionally, in the above graft method (c), the functional group utilizable in the reaction among functional groups in the obtained polyurethane resin is the hydroxyl group alone which is less reactive, and therefore it is difficult to use the resin in further other uses by a chemical modification using this hydroxyl group. Moreover, some reaction steps increase, so that the preparation method is an inconvenient complex.
On the other hand, the resins having the hydroxyl group in a molecule inclusive of the above-mentioned polyurethane resin are usually excellent in flexibility, adhesive properties, coating film formability, the dispersibility of a pigment and the like, and therefore they are often used as binders for coating compositions, ink bases, adhesives, coating materials and the like. Heretofore, for the purpose of imparting mold release properties, sliding properties, water repellency and the like in addition to the above characteristics of the resins having the hydroxyl group, it has been investigated to add the silicone to the resin having the hydroxyl group (Japanese Patent Application Laid-open No. 11117/1989).
However, when a silicone such as a dimethylsiloxane is added to the resin having the hydroxyl group and this resin containing the silicone is used for coating, the resulting coating film is opaque and the surface state of the film is not smooth, because the compatibility between the silicone and the resin is low. In addition, even if the compatibility can be improved, the silicone bleeds out from the resin having the hydroxyl group with the lapse of time, because the silicone does not chemically bond to the above resin. In consequence, the above object cannot be achieved inconveniently.
In order to solve the above problems and to maintain the effect of the added silicone, it has also been suggested to chemically modify the resin having the hydroxyl group with the silicone (Japanese Patent Application Laid-open No. 11117/1989). That is to say, a reactive silicone having an organic functional group such as a carboxyl group or an epoxy group which can react with the hydroxyl group is grafted on the hydroxyl group in the resin. However, this method is not practical, because the reactivity of the silicone is low, and so a large amount of the unreacted silicone remains in a reaction mixture.